1. Field of Invention
The present invention relates to valve stem seal assemblies for use in internal combustion engines, and more particularly to sealing media retainers for such seal assemblies.
2. Description of the Prior Art
Those skilled in the art will appreciate the manner in which intake and exhaust valves are employed in cylinder heads of internal combustion engines. Such valves, supported for reciprocal motion within valve guides, include integral elongated stems extending away from the engine cylinder heads, the ends of the stems interacting with rotating cams for cyclic repeated opening and closure of the valves against the force of valve return springs during the combustion cycle. Obviously, in order to permit unobstructed reciprocal movement of the stem in the guide, some mechanical clearance must exist between the valve guide and the moving stem. The valve stems thus move reciprocally to and from the cylinder head, each within its individual guide, and so-called valve stem seal assemblies are used to seal against leakage of oil through a clearance path between each annular engine valve guide and an associated valve stem.
Thus, and as is well known, the intake port of a combustion chamber is opened and closed by the reciprocating motion of at least one intake valve, which in turn is driven by the rotary motion of a cam, the latter being affixed to and rotatable with an engine camshaft. The intake valve permits fuel mixed with air to flow into the combustion chamber. In addition, an internal combustion engine has at least one exhaust valve and associated exhaust port for releasing expended combustion gases to the atmosphere. Typically, intake and exhaust valves are of similar construction and both include stems integrally affixed to the valves.
In the typical engine, a valve stem seal assembly is fitted over or atop each valve guide, wherein each assembly has a retainer frictionally mounted to an associated valve guide, or is retained in place via cooperation of a return spring and a retainer flange, to assure securement of the assembly within the engine. Typically each valve stem seal assembly has two primary parts; 1) an elastomeric oil seal positioned at one end to control leakage of oil between the valve stem and guide as noted, and 2) a structural cylindrical part called a retainer mounted atop of the valve guide. In many cases, the retainer has a so-called bottom flange that extends circumferentially about the bottom of the valve guide for supporting the retainer on the cylinder head deck. As those skilled in the art will appreciate, the cylinder head deck provides support for the bottom flange on which the noted valve return springs bear.
Much progress has been achieved in the art of valve stem seal assembly design and construction. However, several design issues remain problematic for traditional valve stem seal assemblies. For example, the number of parts associated with a valve stem seal assembly has typically been at least the two described: 1) the seal body, and 2) the retainer. However, more often than not, a third part called a xe2x80x9cgarter springxe2x80x9d is disposed within a circumferential groove about the exterior of the seal body to impart a hoop stress or force to the circumferential sealing lip. One common concern related to the garter spring is that it tends to lose its resilience over a period of time, often short of the useful life of the valve stem seal assembly. Another issue is cost of this typically spring metal part.
The present invention operates to alleviate these issues.
The present invention provides a two-piece valve stem seal assembly for an internal combustion engine. A plurality of such assemblies is contemplated for use in an engine, each assembly designed for insertion over each engine valve guide. Each assembly is adapted for continuous engagement with an associated reciprocally movable valve stem. The elastomer seal body incorporates an interior circumferential aperture containing at least one radially inwardly directed sealing lip adapted to engage the stem to minimize escape of oil lubricant from the engine along a path between the valve guide and the reciprocally movable valve stem seal. The retainer includes a dual finger system for performing two separate functions. Thus, upper and lower sets of circumferentially disposed fingers depend radially inwardly from the cylindrical retainer body, each set of fingers functioning independently of the other, and each set being axially offset from the other. In one preferred form the lower fingers operate to assure retention of the seal body to the top of the valve guide, while the upper fingers, each formed in the shape of a goose neck, extend resiliently against the valve stem seal body to assure that a continuously applied, radially inwardly directed force is applied to the reciprocally moving stem. In one preferred form the lower and upper sets of fingers are adapted to share a common groove disposed about the elastomeric seal body. Finally, to the extent that a more robust and dependable resilient system is offered by this invention, the upper fingers avoid dependence on, and thus fully eliminate, any need for a traditional garter retention spring.